1. Field of the Invention
The present invention relates to a substrate having a fine line, an electron beam substrate utilizing the same, and an image display apparatus employing the same.
2. Related Background Art
There are also known configurations in which a fine line is formed on a substrate. The fine line can be, for example, a cell partition wall between light-emitting cells in a plasma display panel, or a wiring (electrode) for driving a device on a substrate.
In the following there will be shown an example of forming a fine line as a wiring in an electron source substrate.
As the electron source, there is for example known a configuration utilizing a surface conduction electron-emitting device. FIGS. 13A and 13B are respectively a schematic plan view of an electron emitting device and a schematic cross-sectional view along a line 13Bxe2x80x9413B in FIG. 13A.
As shown in FIGS. 13A and 13B, the electron emitting device is principally composed of an insulating substrate 200, electrodes 2, 3 formed by film formation on the substrate 200, an electron-emitting electroconductive film 7 formed by film formation so as to be electrically connected to the electrodes 2, 3, and an electron-emitting region 8 provided in the electron-emitting electroconductive film 7.
As an application of such electron-emitting device, there is known an image forming apparatus such as a display apparatus. FIG. 14 is a partially broken perspective view of an image forming apparatus (image display apparatus) utilizing the surface conduction electron-emitting device shown in FIGS. 13A and 13B.
As shown in FIG. 14, such image display apparatus is provided with a substrate 81, an outer frame 82 and a face plate 86 on which an image forming member (phosphor) 84 is provided, and such outer frame 82, substrate 81 and face plate 86 are sealed at the connecting portions thereof with an unrepresented adhesive material such as low-melting glass frit to constitute an envelope (hermetic container) 88 for maintaining the interior of the image display apparatus in vacuum state.
On the substrate 81, there is fixed a substrate 200 on which electron-emitting devices are formed. On the substrate 200, electron-emitting devices 74 are formed in a matrix arrange nxc3x97m, wherein n and m and positive integers at least equal to 2, and are suitably selected according to the desired number of display pixels.
Each electron-emitting device 74 is connected to a row-direction wiring 4 and a column-direction wiring 6, both consisting of electroconductive films. The wirings shown in FIG. 14 consist of n column-direction wirings 6 and m row-direction wirings 4 (also called xe2x80x9cmatrix wiringsxe2x80x9d). At the crossing region of the row-direction wiring 4 and the column-direction wiring 6 there is provided an unrepresented insulating layer to insulate the row-direction wiring 4 from the column-direction wiring.
In order to form the image display apparatus described above, it is necessary to form a plurality of the row-direction wirings 4 and the column-direction wirings 6.
For forming a plurality of the row-direction wirings 4 and the column-direction wirings 6, it is disclosed, for example in the Japanese Patent Application Laid-open No. 8-34110, to form the wiring composed of an electroconductive film by a printing technology that is relatively inexpensive and is capable of covering a large area without a vacuum apparatus or the like.
For such printing technology, there is usually employed screen printing.
In the screen printing technology, a plate having an aperture of the desired pattern is employed as a mask, and paste containing electroconductive particles such as metal particles is printed through the aperture of the mask onto a substrate constituting the object of printing and is then baked thereby obtaining an electroconductive wiring of the desired pattern.
Also in order to obtain a finer pattern or an improvement in the positional precision which are difficult to attain with the screen printing, there may also be employed a method of employing photosensitive metal paste formed by providing the paste with photosensitive property.
In the method employing such photosensitive metal paste, the photosensitive paste formed as a film on the substrate is exposed to light through a photomask having a desired wiring pattern and is then subjected to development and baking processes thereby forming an electroconductive wiring of the desired pattern.
Among the electron-emitting devices, in addition to the aforementioned surface conduction type electron-emitting device, there are also known, for example, a spint type electron-emitting device having a conical electron-emitting region, and a MIM type electron-emitting device. The electron-emitting device can be utilized as an image display device by a combination with a phosphor which emits light by the electrons emitted by such electron-emitting device. Among the image display devices, there is known, for example, an EL device in addition to the electron-emitting device. Also there is known a configuration in which a micromirror is utilized as an image display device and an image is displayed by integrating such micromirrors and controlling the light reflection by each of such micromirrors. Also there is already widely employed a configuration of utilizing liquid crystal as an image display device for displaying an image.
Another background technology is disclosed in the Japanese Utility Model Application Laid-open No. 5-38874, which discloses, for connecting mutually opposed two conductive films, a technology of superposing a resistive film with each end of the two conductive films. Also there is disclosed a technology of forming the end portion of the conductive film with a straight or curved folding line such as of a sawtooth shape, a comb-tooth shape or an undulating shape in order to prevent a rack in the resistive film at the stepped difference in the superposed region from growing into a large single crack.
Still another background technology is disclosed in the Japanese Patent Application Laid-open No. 8-315723 which discloses a configuration of forming a recess in the wiring and positioning a spacer in such recess.
Formation of a fine line, such as a wiring, consisting of a thick film for example by a printing method on a substrate is associated with the following drawbacks.
In a configuration in which the fine line is formed on the substrate, such fine line may be peeled off from the substrate.
Such phenomenon is considered to result from generation of a stress between the fine line and the substrate.
For example, in case of a wiring formed on a glass substrate is made thick, a crack may be formed in the glass substrate in a region where the end of the wiring is in contact with the substrate (such crack being hereinafter called as an end crack). Also a crack may be generated in the glass substrate in a direction parallel to the longitudinal direction of the wiring (such crack being hereinafter called a side crack).
One of the causes of such phenomena is that, in case an organic component is contained in the composition, such organic component escapes at the baking operation to induce a contraction in the volume, thereby applying a stress to the glass substrate. Another cause is assumed that a stress is applied to the glass substrate by a thermal stress resulting from the difference in the thermal expansion coefficient between the components of the paste and the glass substrate.
Such cracks are formed at the baking process or with the lapse of time thereafter.
Also there may result drawbacks that the aforementioned end crack and side crack respectively extend and are mutually connected to form a large crack or that the wiring itself becomes bent and is peeled off from the substrate.
Such situations will be explained further with reference to FIGS. 15A to 15D, schematically showing the drawbacks resulting the wiring substrate of the conventional technology. FIGS. 15A to 15D schematically show a wiring formed on a substrate, wherein FIG. 15A is a plan view, FIG. 15B is an enlarged perspective view, seen from the rear side, of a circled portion 15B in FIG. 15A, FIG. 15C is a magnified look-through view, seen from the rear side, of encircled portion 15C in FIG. 15A, and FIG. 15D is a cross-sectional view along a line 15Dxe2x80x9415D in FIG. 15A.
The illustrated example shows a case where plural slat-shaped (line-shaped) thick film wirings 1 are formed (baked) on the glass substrate 200.
As shown in FIG. 15B (a magnified look-through view of an encircled portion 15B), side cracks 30 may be generated in the glass substrate 200, substantially parallel to the longitudinal direction of the wiring 1 and along both ends of the width thereof.
Such side crack 30 principally depends on the film thickness and the probability of crack generation becomes higher as the film thickness increases. The cross-sectional shape of the wiring is also an influencing factor. In case of employing photosensitive paste, the cross-sectional shape of the wiring is substantially trapezoidal, but the both lateral faces becomes somewhat thicker than the central portion. For this reason, there are often generated two side cracks slightly inside both ends of the width of the wiring as illustrated.
Also as shown in FIG. 15C (a magnified look-through view of an encircled portion 15C), end cracks may be generated with a shell-shaped pattern at the end of the wiring. Also such end crack 30 depends on the film thickness and the probability of crack generation becomes higher as the film thickness increases.
Also, as shown in FIG. 15D, both end portions 5 of the wiring 1 may be peeled off in a large dimension. The probability of such phenomenon becomes higher as the film thickness increases or as the number of baking process increases.
In case a stress (for example thermal expansion or contraction mentioned above or volume contraction) is applied to the wiring 1, since the wiring 1 is adhered thereto, a tensile force or the like is transmitted to the substrate 200 thus leading to a crack if the adhesive force is large or a peeling if the adhesive force is small.
The aforementioned crack or peeling of wiring tends to be generated when the film thickness after baking is at about 10 xcexcm, and the probability of generation of such crack or peeling and the level thereof becomes higher as the film thickness increases for example to 12 xcexcm or 18 xcexcm.
Such end crack or peeling of wiring leads, in the lead portion of the wiring, to a drawback that a flexible circuit board or a tab cannot be mounted by peeling thereof together with the wiring at the succeeding mounting operation of such flexible circuit board or tab, or, in other portion, a drawback of shortcircuiting resulting from that the end portion of the wiring is bent up to come in contact with other portions or resulting from the chipping or dropping of the wiring, or a drawback that the shape of markers such as an alignment mark becomes unstable.
The present application discloses an invention of which an effect is to suppress the peeling of the fine line and the crack generation in the substrate.
One of the inventions relating to the substrate having the fine line of the present application is featured by:
a substrate having a fine line, wherein the fine line is provided, in at least a part in the longitudinal direction thereof, with plural recesses arranged with a gap not exceeding 200 xcexcm.
The presence of such recess allows to disperse the stress generated in the fine line or at the interface between the fine line and the substrate.
In particular, the aforementioned plural recesses are preferably arranged in a direction crossing the longitudinal direction of the fine line (namely a direction not parallel to the longitudinal direction of the fine line, and the gap between the end of the fine line and the recess adjacent to such end does not exceed 200 xcexcm in a direction passing through the plural recesses and perpendicular to the longitudinal direction of the fine line. Wherein, the above xe2x80x9cplural recesses are arranged in a direction crossing the longitudinal direction of the fine linexe2x80x9d means a configuration that the plural recesses are arranged in a sectional area along the direction crossing the longitude of the fine line. Such configuration of the structure is for example shown in FIGS. 1A, 1B, 1E and 1F.
Also in the aforementioned invention, between the recesses and/or between the end of the fine line and the recess in a direction passing through the recesses and perpendicular to the longitudinal direction of the fine line there exists a portion thicker than the thickness of the recess (namely the distance between the bottom of the recess and the surface of the substrate on which the fine line is formed), and such thickness of the recess preferably does not exceed 15 xcexcm, more preferably 10 xcexcm. Also the thickness of the recess is preferably at least equal to 30 nm.
Also in the aforementioned invention, there can be advantageously adopted a configuration in which the aforementioned recess is formed as a groove extending in the longitudinal direction of the fine line and a configuration in which such groove is arranged in plural units in mutually parallel manner.
The aforementioned invention can be particularly advantageously applied to a configuration where the aforementioned fine line is utilized as a wiring.
Also the aforementioned invention is particularly effective in case the fine line is obtained by applying paste-like material onto the substrate and then heating such material.
The present application also includes the following invention:
a substrate having a fine line, wherein the fine line is provided with a recess in at least a part thereof, wherein the width of the fine line in a direction passing through the recess and perpendicular to the longitudinal direction of the fine line is 200 xcexcm or larger.
This invention may be advantageously used in combination with the foregoing inventions.
The present application further includes the following invention:
a substrate having a fine line, wherein the fine line is provided in at least a part in the longitudinal direction thereof, with plural recesses arranged in a direction crossing the longitudinal direction of the fine line.
Also this invention may be advantageously used in combination with the foregoing inventions.
In the foregoing inventions, the recess is preferably provided in all the portion of the fine line where the width of the fine line, in a direction perpendicular to the longitudinal direction thereof, is 200 xcexcm or larger, but it may also be provided only in a particularly necessary portion such as the longitudinal end portion of the fine line. For example the longitudinal end of the fine line is apt to be subjected to an external force by a succeeding process such as connection to another member and therefore tends to generate peeling, so that the configuration having the recess of the present invention can be advantageously adopted.
Also the present application includes an invention for a configuration in which the fine line provided on the substrate is utilized as a wiring for driving an electron-emitting device. More specifically, such configuration can be realized by providing an electron-emitting device on the aforementioned substrate, electrically connecting the fine line, constituting the wiring, with the electron-emitting device and supplying a voltage for causing the electron-emitting device to emit electrons through the wiring.
Furthermore, the present application includes an invention for a configuration in which the aforementioned electron source is combined with a phosphor emitting light by the electrons emitted by the electron-emitting device to constitute an image display apparatus.
Furthermore the present application includes an invention for a method for forming a wiring on a substrate, the method comprising:
a step of forming a film of photosensitive electroconductive paste to constituting the wiring;
a step of irradiating the formed film of the electroconductive paste with light through a photomask bearing a pattern similar in shape to the recess to be formed on the surface of the wiring;
a development step after the light irradiation; and
a baking step after the development step.
Also the wiring forming method of the present invention comprises:
a step of printing conductive paste on the substrate, utilizing a plate bearing a pattern similar in shape to the recess to be formed on the surface of the wiring; and
a baking step after the printing.
Also the wiring forming method of the present invention comprises:
a step of forming a wiring on the substrate; and
a step of eliminating a part of the formed wiring thereby forming a recess.